GB1406889A - Video signal output of an opto-electronic transducer to simulate the effect of an electrical filter on said video signal - Google Patents

Abstract

1406889 Diffraction grating PHILIPS ELECTRONIC & ASSOCIATED INDUSTRIES Ltd 11 Aug 1972 [14 Aug 1971] 37551/72 Heading G2J [Also in Division H4] In the field-sequential colour-television camera described in Specification 1293315 with reference to Figs. 1, 2 and 4 thereof, the frequency spectrum, Fig. 2, of the definition reduced luminance signal Y<SP>1</SP> produced by electronically removing the high frequency content CY from the full frequency range luminance signal Y, is different from that (Y) produced by the matrix combination of the reduced definition chrominance signals R, G, B. A point source L, Fig. 1, produces a luminance distribution across a scanned line of the camera tube target 3 as shown in Fig. 5a yielding a luminance signal at A having a corresponding shape and lasting 100ns between half power points. The removal of the high frequency content CY from this signal at 9, yields the broadened Gaussion shaped pulse of Fig. 5b. It is therefore an object of the invention to optically reduce the definition of the chrominance signals such that the signal Y has the same shape and extent as that of Y<SP>1</SP> in Fig. 5b. Each colour section of the rotating filter 1, Fig. 3 is covered with a series of sections of diffraction gratings, the gratings in each sector having different spacings. The spacings of the gratings are calculated such the following action takes place. The light distribution of Fig. 5a is diffracted by the grating Z=1 through an angle of α, Fig. 4 to give two first order diffraction distributions I 11 , as well as the zero order, non diffracted distribution I 01 . Similarly the light distribution of Fig.5a is diffracted by the gratings Z = 2, 3-6, to give the respective first order distributions I 12 , I 13 , I 14 ... I 16 as well as the undiffracted zero order distributions I 02 - I 06 . The diffracted light distributions are integrated by the target of the camera tube so that an 'envelope' distribution is produced having the required shape and extent of Fig. 5b. A phase grating is preferable, since it allows greater control of the diffraction characteristics, although a black and white grating may be used.